The present invention relates to an information processing apparatus and, more particularly, to an apparatus which executes an information transfer.
The transferring of information from one unit to another unit is an important element in many information processing apparatuses. Information transfer is very frequently performed in the information processing apparatus comprising a memory unit, a central processing unit (CPU), and a peripheral unit or peripheral control unit. The information transfer, in the early days of the computers, was performed only under control of the CPU. In such a case, a CPU executes the information transfer processing in accordance with a program. For executing the transfer processing by the CPU a time period of one information transfer was very long, for example, 42 clocks. This is a serious problem in an apparatus requiring the data transfer at a high speed such as an image processing system.
On the other hand, a direct memory access (DMA) unit is well known as a data transfer control unit which executes a data transfer without using a CPU. This control unit can execute a data transfer from one unit to another unit in about 4 to 5 clocks. However, this control unit has to control the one and the other units at different timings, and therefore when a larger number of data must be transferred, or an address of the transfer unit is different from an address of the receiver unit, the operation of the control unit is very complicated. Additionally, in these cases, the speed of the data transfer is slow so that the control unit can not be used in the image processing system in which a high-speed data transfer is required.